Route thumbnail and node image texture setup through helpers

docs/modernization/roadmap.md

@@ -3021,6 +3021,10 @@ Results:
   stroke composite shader setup helper, while render-task ordering, framebuffer
   copy bounds, sampler/texture binding, and draw execution remain in retained
   canvas-mode code.
+- `Canvas::thumbnail_generate` checkerboard redraw and final texture blending
+  now share the retained draw-merge shader setup helpers, while destination
+  copies, sampler/texture binding, readback, and draw execution remain in
+  retained Canvas code.
 - `Canvas::draw_objects` retained object compositing now shares the retained
   draw-merge texture shader setup helper, while temporary face readback,
   sampler/texture binding, draw execution, and dirty-box updates remain in
@@ -3032,6 +3036,10 @@ Results:
   draw-merge shader setup helper for per-layer `TextureBlend` uniforms, while
   destination feedback copies, sampler/texture binding, grid redraw, readback,
   and draw execution remain in retained Canvas code.
+- `NodeImage` and `NodeImageTexture` retained plain image drawing now share the
+  retained draw-merge texture shader setup helper for `Texture`, `Tex`, and
+  `MVP` setup. Texture/sampler binding, atlas setup, blend state, and draw
+  execution remain in the node paths.
 - `Canvas::stroke_draw_mix` now shares the retained stroke composite shader
   helper for mixer-pass `CompDraw` setup, while preserving its caller-specific
   texture slot uniforms. Mixer framebuffer/scissor state, sampler and texture